1. Field of the Invention
The present invention relates to a nitride semiconductor light-emitting device having a nitride-based III-V group compound semiconductor layer and a facet coat formed at a facet of an optical resonator.
2. Description of Related Art
In recent years, increasingly high capacities and hence increasingly high densities have been sought in optical disks. Accordingly, standards on BDs (Blu-ray discs) and HD-DVDs (high definition DVDs) using a blue semiconductor laser have been worked out, and products such as decoders therefor have been developed. Demands have been made for reliable high-output blue semiconductor lasers to achieve data writing to such novel disks at increasingly high densities (to cope with two-layer disks) at accordingly high speeds.
In conventional AlGaAs- or InGaAlP-based semiconductor lasers that read data from and write data to CDs or DVDs, optical resonator facets are coated with a dielectric film such as SiO2, Si3N4, or Al2O3 to prevent them from degrading or being optically damaged. When this method was applied in a blue semiconductor laser, the drive current was observed to suddenly rise. This is the reason that improvement in a coating technique has been sought after.
Japanese Patent Application Laid-Open No. 2002-335053 reveals that one of the causes of degradation of an optical resonator facet is poor adhesion between the optical resonator facet and a facet coat, and hence proposes a method of forming a facet coat at an optical resonator facet with a metal adhesion layer placed therebetween.
However, when a metal film is used as an adhesion layer, a short circuit occurs in a pn junction on the optical resonator facet, leading to greater absorption of light. The nitride semiconductor laser oscillates at a short wavelength and emits high-energy light, and therefore its output facets degrade due to slight absorption of light. This makes it difficult to realize a high output device with an optical output of more than 100 mW. On the other hand, from the viewpoint of preventing a short circuit in the pn junction and absorption of light, the film thickness needs to be so controlled as to be 10 nm or less, further preferably 5 nm or less, still further preferably 2 nm or less. In that case, the difficulty of film thickness control results in lower yields.